Lymphoid cellular responses in the blood after immunization in man.

A combined morphological and metabolic study has been made of the lymphoid cells in the blood during the immune response in man. Similar changes were observed in both primary and secondary responses to a number of different microbial antigens. The cellular response involved an increase in numbers of three types of cell; hyperbasophilic medium lymphocytes, plasma cells, and large lymphoid cells. The large lymphoid cells were about 20 micro in diameter with large nuclei, prominent nucleoli, and an intensely basophilic cytoplasm with numerous polyribosomes. About 30% of these cells were in the DNA synthetic phase of cell growth. Electron microscopy has shown that many of the basophilic medium-sized cells have sufficient well-organized endoplasmic reticulum to be included in the plasma cell series. The hyperbasophilic cells labeled more heavily with tritiated uridine and tritiated leucine than the normal small and medium lymphocytes from the peripheral blood of patients not under antigenic stimulation. The evidence in this paper supports the argument that the atypical mononuclear cells first described by Türk and others in the blood of patients with infections are immunoblasts, plasma cells, and other reactive lymphoid cells representing a circulating population of lymphoid cells derived from lymphoid tissue responding to antigenic stimulation. The presence of such cells may be a valuable indication that an immunological reaction is in progress when direct proof is lacking.